SIOUX FALLS, S.D. (AP) — Six couples have filed a federal lawsuit to block South Dakota's ban on same-sex marriage, leaving North Dakota as the only state in the country with an unchallenged ban.

The lawsuit was filed Thursday in U.S. District Court in Sioux Falls.

It challenges both South Dakota's ban on gay marriage and its refusal to recognize marriages of same-sex couples who legally wed in other states.

The lawsuit means cases are currently pending in 30 states with gay marriage bans. Judges have overturned several of those bans since the U.S. Supreme Court struck down part of the federal Defense of Marriage Act last year.

Minneapolis-based attorney Josh Newville is representing the South Dakota couples. He says he's also seriously considering filing a similar challenge in North Dakota.